1. Field of the Invention
The present invention relates generally to an apparatus for grinding and, more particularly, to such an apparatus of the type wherein a rotating grinding wheel is advanced toward a spindle-mounted workpiece under the control of a microprocessor which responds to workpiece diameter signals.
2. Description of the Prior Art
The previously known grinding machines typically comprise a circular grinding wheel adapted to rotate about an axle and a spindle adapted to hold a workpiece at a position radially spaced from the grinding wheel. The spindle also rotates the workpiece about its axis.
The grinding wheel is mounted on a table which is radially movable so that the grinding wheel can be moved into contact with the workpiece on the spindle. Contact of the grinding wheel with the workpiece, of course, initiates the grinding operation and removes material from the workpiece in the conventional fashion. The rotation of the workpiece on the spindle is necessary to insure that the material removed from the workpiece is evenly distributed around the workpiece, thus, grinding a true diameter on the workpiece.
Although any of a number of means may be utilized to advance the table supporting the grinding wheel toward the workpiece on the spindle, typically a threaded shaft cooperates with a threaded boss on the table. Consequently, rotation of the threaded shaft in a first rotational direction advances the grinding wheel toward the workpiece while, conversely, rotation of the shaft in the other direction retracts the grinding wheel from the workpiece. Likewise, the speed of rotation of the shaft is directly proportional to the lineal or radial speed of the grinding wheel toward or away from the workpiece.
In the previously known grinding machines, the grinding wheel is advanced towards the workpiece either manually or at a constant and predetermined lineal rate obtained from a steady state rotation of the shaft. The degree of advance is controlled either by hand or by a controller having the capability to receive and store end point coordinates for the movable components.
Many previously known grinding operations typically comprise two separate grinding operations, namely a rough grinding operation and a finish grinding operation. In the rough grinding operation, the grinding wheel is advanced towards the workpiece at a given lineal speed, for example, 0.004 inches per second which removes most of the excess material from the workpiece. The finish grinding operation occurs subsequently and in this operation the grinding is also moved towards the workpiece in the above-described fashion but at a much slower rate, typically 0.0005 inches per second. A lesser amount of material is removed from the workpiece during the finish grinding operation than in the rough grinding operation but a smoother finish on the workpiece and more accurate control of the workpiece diameter is obtainable during the finish grinding operation.